Triglycerides occur as normal constituents of all forms of animal, vegetable and marine life. The fats of sea life are characterized by the presence of high molecular weight, highly unsaturated acids associated with only minor amounts of saturated acids. In contrast, the fats of land animals contain large amounts of C.sub.16 and C.sub.18 saturated and unsaturated acids, whereas fats of vegetable origin contain substantial amounts of closely related acids which are characteristic of a particular source.
Our ancestors developed many specific uses for fats in addition to their use as foods. It is believed that saponification was the first chemical reaction to which oils and fats were subjected, and the early chemical history of these substances actually constitutes a study of this process. The products of saponification offered the initial clue to the actual structure of the fats. Soaps were first prepared by boiling fats with wood ashes and were considered to be a combination of the fats with the ash constituents. Later, caustic was substitued for the wood ashes. The first United States patent was issued in 1790 to Samuel Hopkins, as signed by George Washington, and it covered the making of pearl-ash as an ingredient of soap manufacture.
It is necessary to go far back into chemical history in order to retrace the various contributions which have culminated in our present ideas concerning fats and saponification. More recently, however, improvements in partial saponification of fats were made. For example, when mixtures of salts of fatty acids and esters of fatty acids are produced by partial saponification, there is a tendency of the salts (soaps) to separate into curds. U.S. Pat. No. 4,824,583 issued in 1989 and it concerns the problem of incompatibility of soaps and esters produced during partial saponification. In order to produce soaps and esters as a homogeneous composition, oxidized polyethylene was used during partial saponification. It was believed that the oxidized polyethylene, particularly the functional carboxyl groups, reacted with components of the saponification mixture to form esters which were believed to promote homogeneity of the composition. Furthermore, in this '583 patent, the partially saponified triglycerides resulting from the reaction with oxidized polyethylene were used as lubricants in rigid PVC compositions.
In brief, hydrolysis of triglycerides with alkaline or alkaline earth metal bases is ancient. The reaction produces glycerol and a mixture of metal salts when one hundred percent of the saponification of the starting triglyceride is achieved. When saponification is less than one hundred percent, mono-substituted and di-substituted glycerides are obtained with triglycerides. However, there has been very little activity as represented by the above '583 patent for the use of partial saponification products as polymer additives. This may be in part attributable to the evolution of the metallic stearate and glyceryl ester industries because both of these industries predate polymers and plastics industries. In the continuing search for more cost-effective solutions in non-polymer areas, high-purity stearate products evolved first. By the time polymer applications became commercial opportunities, additives manufacturers had production facilities dedicated to making high-purity products.
Against this background, this invention is directed to improvements in partially saponified triglycerides, their methods of manufacture and applications as polymer additives.